JXB Advance Access published online on December 19, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern331
RESEARCH PAPER |
A segment containing a G-box and an ACGT motif confers differential expression characteristics and responses to the Arabidopsis Cytc-2 gene, encoding an isoform of cytochrome c
1Cátedra de Biología Celular y Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, CC 242 Paraje El Pozo, 3000 Santa Fe, Argentina
2Division of Applied Life Science (BK21 program), Environmental Biotechnology Research Center, Gyeongsang National University, 900 Gajwa-dong, Jinju, Gyeongnam 660-701, Republic of Korea
* To whom correspondence should be addressed: E-mail: dhgonza{at}fbcb.unl.edu.ar
Sequences required for the expression of Cytc-2 (At4g10040), one of two cytochrome c genes from Arabidopsis thaliana, were characterized using plants transformed with deleted and mutagenized promoter fragments fused to gus. These studies indicated that a region containing a G-box and an ACGT motif is essential for expression. Mutation of the ACGT motif causes a complete loss of expression, while mutation of the G-box causes decreased expression in aerial parts and abolishes expression in roots and induction by environmental factors. Upstream located site II elements are required for maximal expression, mainly in reproductive tissues, and maximal induction by different factors. One-hybrid screenings allowed the identification of transcription factors from the bZIP and bHLH families that interact mainly with the G-box. Four of these factors were able to bind to the Cytc-2 promoter in vitro and in transactivation assays in Arabidopsis. Analysis of available microarray data indicated that the bZIP transcription factors share expression characteristics with the Cytc-2 gene, suggesting that they act as mediators of its response to tissue-specific, environmental, and metabolic conditions. Site II elements interact with a TCP family protein and may co-ordinate the expression of the Cytc-2 gene with that of other respiratory chain components. A model is proposed for the evolution of the Cytc-2 gene through the incorporation of a segment containing a G-box and an ACGT motif into an ancestral gene that contained site II elements. This may have reduced the importance of site II elements for basal expression and conferred new responses to environmental factors.
Key words: Arabidopsis thaliana, cytochrome c, mitochondrion, promoter analysis
Received 29 September 2008; Revised 24 November 2008 Accepted 24 November 2008
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